Considering the fact that optical fibers may have an outside diameter of 125 microns, the connection of two optical fibers such that their cores in the range of about 8 to 50 microns are aligned is a formidable task. Several connectors are available commercially for establishing a connection between optical fibers.
One connector is referred to as a biconic connector. It includes facilites for holding two plugs each of which terminates an optical fiber and each of which has a conically shaped end portion. The optical fiber end terminates in a pedestal which extends beyond an end face of the plug. Two plugs are received in opposite ends of a sleeve which is mounted in a housing. The sleeve includes opposed, conically shaped cavities for receiving the plugs and for holding them in a manner to cause the end faces of the optical fibers to touch or to be spaced apart slightly. The plugs and the sleeves, which are molded, are controlled such that their mating surfaces cause the optical fibers to become aligned when the plugs are received in the sleeve. In this connector, the plugs are free to be turned about their longitudinal axes. Generally, facilities are not provided for repeated alignment of the plugs with respect to the sleeve.
Another connector is referred to as a ferrule type connector. It includes a coupler having a plug-receiving tubular portion at each end thereof. Each tubular portion is provided with a slot which extends longitudinally therealong. A sleeve which floats within the coupler is adapted to receive coaxially two plugs each of which is adapted to terminate an optical fiber. Each plug has a passageway extending longitudinally therethrough for receiving an optical fiber and is mounted in a connector body having an alignment pin projecting radially therefrom. When the connector body is received in a tubular portion of the coupler, the alignment pin is received in the slot which extends along the tubular portion. An assembly pin which projects radially from each tubular portion of the coupler is received in a slot of a housing which encloses the associated plug and connector body and which encloses a tubular portion of the coupler when the plug is assembled to the coupler. The slot in the housing includes a circumferential portion in which the assembly pin of the coupler is received to lock the plug to the coupler.
The ferrule type connector is advantageous in that the plugs are made of a ceramic material and are not molded. As a result, the plugs may be machined with close tolerances which is advantageous when dealing with optical fibers having relatively small dimensions. Further, the passageways in the plugs that are destined to receive the optical fibers are made cleanly without the molding flash which may be expected in other kinds of connectors and which could damage the optical fibers.
Although the floating sleeve in the coupler of the ferrule type connector assures that the outer surfaces of the plugs are aligned, it does not insure that the passageways in the plugs are aligned. Of course, if the passageways are not aligned, the optical fibers which are received in the passageways are not aligned and transmission losses ensue.
The prior art includes a connector system having a positioning tab which assures the same radial alignment of the ends of the optical fibers after repeated couplings. This insures that the fiber ends after disconnecting and reconnecting are always coupled together with the same orientation as before disconnection, but it does not provide for optimal alignment of the optical fibers in the first instance. Of course, optimal alignment may be achieved by a trial and error process which involves testing for each iteration of the process.
What is needed and what is not provided by the prior art is a ferrule type system for connecting optical fibers in which provisions are made for causing the optical fibers to be aligned optimally. A solution to the problem should be one which is relatively inexpensive to carry out, and should be one which is compatible with the presently available ferrule type connectors.